The attached document presents the difference pronunciations of the ed suffix used to form past and past participles of regular verbs. It includes a narration so that you understand the difference among these sounds. Once you review the document, please add your opinion.
https://docs.google.com/leaf?id=0Bx00-D2TyB94Yzg1ZTBmYzctOWU2MC00MzI3LTg3ZDgtYmVlNjFlMTkyZTk4&hl=en
Enjoy it!